1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus.
2. Description of Related Art
In general, an electrophotographic image forming apparatus (such as a printer, a copy machine, and a fax machine) is configured to irradiate (expose) a uniformly-charged photoconductor (for example, a photoconductor drum) with (to) laser light based on image data to form an electrostatic latent image on the surface of the photoconductor. The electrostatic latent image is then visualized by supplying toner from a developing device to the photoconductor on which the electrostatic latent image is formed, whereby a toner image is formed. Further, the toner image is directly or indirectly transferred to a sheet through an intermediate transfer belt, followed by heating and pressurization for fixing at a fixing section, whereby an image is formed on the sheet.
Such an image forming apparatus has conveyance guides that respectively face the front and rear surfaces of a sheet. A sheet feeding path is formed by the conveyance guides, and a sheet is conveyed along the sheet feeding path. In addition, for the purpose of downsizing the apparatus and adopting duplex image formation, the sheet feeding path is curved to a certain extent. At a curving part having a large curvature, and a part where the curvature changes in the sheet feeding path, a conveyance rolling part having a small frictional coefficient and protruding from the conveyance guide toward the inside of the sheet feeding path is disposed (see, for example, Japanese Patent Application Laid-Open Nos. 2002-316748 and 2011-102157). The conveyance rolling part is a rotating member that makes contact with a conveyed sheet and rotates along the sheet, and examples of the conveyance rolling part include a conveyance rolling part having one wide rolling member extending in the sheet width direction, and a conveyance rolling part having a plurality of narrow rolling members juxtaposed along the sheet width direction.
In recent years, demand for high image quality is strong, and only a small damage on the image forming surface, which has caused no problem in the past, may cause problems, especially in the field of production printers used for commercial printing such as on-demand printing. Meanwhile, the types of sheets used in commercial printing have been diversified to include sheets (coated sheets, for example) whose image forming surface is easily damaged. In the case where a coated sheet is used, the image forming surface of the sheet can be damaged by just making contact with the guide member, and such damage easily stands out.
As illustrated in FIGS. 1A and 1B, in a conventional image forming apparatus, a plurality of conveyance rolling parts 32 to 34 are disposed on the image forming surface side of the sheet at curving part 165R of sheet feeding path 165. A sheet output from conveyance roller section 31 is conveyed in contact with conveyance rolling parts 32 to 34, and therefore the image forming surface of the sheet does not make contact with conveyance guide 35 or 36.
In addition, in view of avoiding corner folding of the sheet, the entering angle of the sheet to the conveyance rolling part is preferably small. For this reason, a conveyance rolling part having a large diameter like conveyance rolling part 33 is often used. At this time, rolling members 321, 331 and 341 of conveyance rolling parts 32 to 34 may overlap each other in the sheet conveyance direction due to a limited installation space. In this case, rolling members 321, 331 and 341 of conveyance rolling parts 32 to 34 are disposed in a staggered manner in the sheet width direction such that conveyance rolling part 32, conveyance rolling part 33 and conveyance rolling part 34 do not interfere each other (see FIG. 1B).
As described above, when a sheet is conveyed with the configuration where rolling members of conveyance rolling parts adjacent to each other are disposed in a staggered manner, an end portion of the sheet in the sheet width direction and an end portion of the rolling member overlap each other, and as a result, sheet conveyance failure may be caused. For example, when rolling members 321, 331 and 341 are disposed such that A5 sheets and A3 sheets can be used with no problem as illustrated in FIG. 2A and FIG. 2B, an end portion of the sheet in the sheet width direction and an end portion of rolling member 331 may overlap each other when A4 sheets are conveyed as illustrated in FIG. 2C.
In view of this, it is preferable to configure the conveyance rolling parts such that end portions of the sheet in the sheet width direction do not overlap with any end portions of the rolling members regardless of the size of the sheet. However, non-uniformity among the components of the image forming apparatus, non-uniformity caused at the time of installation, and non-uniformity in position of the sheets during conveyance in the sheet width direction are unavoidable, and therefore it is difficult to achieve a design in which end portions of the sheet in the sheet width direction and end portions of the rolling members do not overlap each other regardless of the size of the sheet.